The disclosure of Japanese Patent Application No. 2000-225615 filed on Jul. 26, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an intake air oxygen concentration sensor calibration device and method that calibrates an output of an oxygen concentration sensor that is provided in a prescribed arrangement along an intake passageway of an internal combustion engine and detects concentration of oxygen contained in intake air.
2. Description of the Related Art
There is available art that is intended to enhance accuracy in control of the air-fuel ratio of internal combustion engines by providing an oxygen concentration sensor in a prescribed arrangement along an intake passageway of the internal combustion engine to detect oxygen concentration in intake air and using the oxygen concentration data detected for controlling operations of the internal combustion engine. One such arrangement is disclosed in Japanese Patent Application Laid-Open Publication No. 11-2153.
The output of the oxygen concentration sensor, however, varies with time and operating conditions (such as engine loads and purge conditions of trapped fuel) of the internal combustion engine. If control is provided for operations of the internal combustion engine, such as air-fuel ratio control, based on variable outputs as those noted above, it is not possible to provide accurate control, which could result in deteriorated exhaust emissions and driveability.
In view of the foregoing, it is an object of this invention to provide an intake air oxygen concentration sensor calibration device and method that calibrates an output of an oxygen concentration sensor that is provided in a prescribed arrangement along an intake passageway and detects concentration of oxygen contained in intake air, thereby allowing control of high accuracy to be provided.
A first aspect of this invention is an intake air oxygen concentration sensor calibration device that is provided with an oxygen concentration sensor provided in a prescribed arrangement along an intake passageway of an internal combustion engine to detect concentration of oxygen contained in intake air, intake passageway pressure detection means that detects pressure in the intake passageway, stable condition determination means that compares the amplitude of fluctuations in intake passageway pressure detected by the intake passageway pressure detection means with a predetermined stable condition criterion value previously stored in memory to determine whether the intake passageway pressure is in a stable condition, calibration coefficient calculation means that calculates a calibration coefficient used to calibrate the output of the oxygen concentration sensor based on the intake passageway pressure detected by the intake passageway pressure detection means and a reference output value of the oxygen concentration sensor previously stored in memory, and calibration means that calibrates the output of the oxygen concentration sensor based on the calibration coefficient calculated by the calibration coefficient calculation means, wherein the stable condition criterion value is set so that the smaller the intake passageway pressure detected by the intake passageway pressure detection means, the smaller the value is, and the greater the intake passageway pressure detected by the intake passageway pressure detection means, the greater the value is, and the calibration coefficient calculation means updates the calibration coefficient when the stable condition determination means determines that the intake passageway pressure remains stable.
According to the first aspect, the stable condition criterion value is set small when the intake passageway pressure detected by the intake passageway pressure detection means stays in a region of small values (and the stable condition criterion value is set large when the intake passageway pressure detected by the intake passageway pressure detection means stays in a region of large values). This permits a precise determination to be made to determine whether the intake passageway pressure remains stable, that is, whether it is in a condition in which, when the calibration coefficient is to be calculated based on the output of the oxygen concentration sensor, the calculation of the calibration coefficient is less susceptible to effects of errors such as a response lag of the oxygen concentration sensor. Results of detection of greater accuracy can therefore be obtained by calibrating the output of the oxygen concentration sensor by using the calibration means while the intake passageway pressure remains stable (or when the calculation of the calibration coefficient is less susceptible to effects of errors such as a response lag of the oxygen concentration sensor).
A second aspect of this invention is an intake air oxygen concentration sensor calibration device that is provided with an oxygen concentration sensor provided in a prescribed arrangement along an intake passageway of an internal combustion engine to detect concentration of oxygen contained in intake air, intake passageway pressure detection means that detects pressure in the intake passageway, calibration coefficient calculation means that calculates a calibration coefficient used to calibrate the output of the oxygen concentration sensor based on the intake passageway pressure detected by the intake passageway pressure detection means and a reference output value of the oxygen concentration sensor previously stored in memory, and calibration means that calibrates the output of the oxygen concentration sensor based on the calibration coefficient calculated by the calibration coefficient calculation means, wherein the calibration coefficient calculation means stores in memory the intake passageway pressure when the calibration coefficient is updated and updates the calibration coefficient only when the intake passageway pressure detected by the intake passageway pressure detection means is greater than the intake passageway pressure when the calibration coefficient was updated last.
According to this second aspect, an error contained in the output of the oxygen concentration sensor accounts for a smaller percentage of the entire output of the oxygen concentration sensor when the output is greater, and the oxygen concentration sensor has a characteristic that the higher the pressure detected, the higher the output it produces even with the same oxygen concentration. It is therefore possible not to update the calibration coefficient when the intake passageway pressure is smaller than that when the calibration coefficient was updated last, thereby maintaining the last calibration coefficient, which is considered to have greater accuracy. When the intake passageway pressure is greater than that when the calibration coefficient was updated last, on the other hand, it is possible to calculate anew the calibration coefficient that has greater accuracy.
A third aspect of this invention is an intake air oxygen concentration sensor calibration device that is provided with an oxygen concentration sensor provided in a prescribed arrangement along an intake passageway of an internal combustion engine to detect concentration of oxygen contained in intake air, intake passageway pressure detection means that detects pressure in the intake passageway, calibration coefficient calculation means that calculates a calibration coefficient used to calibrate the output of the oxygen concentration sensor based on the intake passageway pressure detected by the intake passageway pressure detection means and a reference output value of the oxygen concentration sensor previously stored in memory, and calibration means that calibrates the output of the oxygen concentration sensor based on the calibration coefficient calculated by the calibration coefficient calculation means. The intake air oxygen concentration sensor calibration device according to the third aspect is further provided with air-fuel ratio detection means that is provided in a prescribed arrangement on an exhaust passageway of the internal combustion engine to detect an exhaust air-fuel ratio of an exhaust gas and calibration coefficient correction means that corrects the calibration coefficient based on an air-fuel ratio feedback correction coefficient calculated from the exhaust air-fuel ratio detected by the air-fuel ratio detection means or the exhaust air-fuel ratio itself detected by the air-fuel ratio detection means.
According to the third aspect, the calibration coefficient calculated based on the intake passageway pressure developing on the intake side of the internal combustion engine is further corrected by using the information obtained based on the exhaust air-fuel ratio on the exhaust side. Calibration of the output of the oxygen concentration sensor according to the calibration coefficient is then corrected through feedback of the information on the exhaust side, which permits calibration of even greater accuracy. The information based on the exhaust air-fuel ratio on the exhaust side may be the exhaust air-fuel ratio itself, or the air-fuel ratio feedback correction coefficient produced as a result of detection made by the air-fuel ratio detection means.
A fourth aspect of this invention is an intake air oxygen concentration sensor calibration device that is provided with an oxygen concentration sensor provided in a prescribed arrangement along an intake passageway of an internal combustion engine to detect concentration of oxygen contained in intake air, intake passageway pressure detection means that detects pressure in the intake passageway, calibration coefficient calculation means that calculates a calibration coefficient used to calibrate the output of the oxygen concentration sensor based on the intake passageway pressure detected by the intake passageway pressure detection means and a reference output value of the oxygen concentration sensor previously stored in memory, and calibration means that calibrates the output of the oxygen concentration sensor based on the calibration coefficient calculated by the calibration coefficient calculation means. The intake air oxygen concentration sensor calibration device according to the fourth aspect is further provided with warm-up completion determination means that determines whether or not the internal combustion engine has completed warming up and the calibration coefficient calculation means updates and stores in memory the calibration coefficient only when the calibration coefficient obtained through calculation is greater than that of the previous update and, at the same time, the warm-up completion determination means determines that the internal combustion engine has completed warming up.
According to the fourth aspect, the calibration coefficient is updated and stored in memory only when an accurate calibration coefficient not affected by blow-by gas is obtained through calculation, which permits calibration of even greater accuracy. The blow-by gas containing unburned fuel can at times be recirculated to an upstream side of the intake passageway. In a condition immediately after a cold internal combustion engine has been started, in which the internal combustion engine still remains cold, however, the concentration of unburned fuel contained in the blow-by gas are so low it is negligible. The fact that the calibration coefficient obtained through calculation is greater than that previously obtained means that the calculation has been made accurately thanks to the intake air not affected by unburned fuel contained in the blow-by gas leaner than in the previous update. Calibration of even greater accuracy can therefore be made by allowing the calibration coefficient to be updated and stored in memory only when the calibration coefficient obtained through calculation is greater than that of the previous update and, at the same time, the warm-up completion determination means determines that the internal combustion engine has completed warming up.
A fifth aspect of this invention is an intake air oxygen concentration sensor calibration device that is provided with an oxygen concentration sensor provided in a prescribed arrangement along an intake passageway of an internal combustion engine to detect concentration of oxygen contained in intake air, intake passageway pressure detection means that detects pressure in the intake passageway, calibration coefficient calculation means that calculates a calibration coefficient used to calibrate the output of the oxygen concentration sensor based on the intake passageway pressure detected by the intake passageway pressure detection means and a reference output value of the oxygen concentration sensor previously stored in memory, and calibration means that calibrates the output of the oxygen concentration sensor based on the calibration coefficient calculated by the calibration coefficient calculation means. The intake air oxygen concentration sensor calibration device according to the fifth aspect is further provided with a fuel storage tank that stores fuel for the internal combustion engine and fuel vapor purge means that traps fuel vapors in the fuel storage tank and supplies it to the intake passageway. The calibration coefficient calculation means replaces the calibration coefficient obtained through calculation with a lower limit guard value pre-stored in memory when the calibration coefficient calculated by the calibration coefficient calculation means while purging of the trapped fuel to the intake passageway by the fuel vapor purge means is not being carried out is the lower limit guard value or less.
According to the fifth aspect, an effect that would be produced if calculation of the calibration coefficient were inaccurate can be minimized. If the calibration coefficient is small, it is possible, however, that the actual output of the oxygen concentration sensor is made small for some reason. It is at the same time possible that the calibration coefficient is not accurately calculated. If the calibration coefficient obtained through calculation is found to be smaller than the lower limit guard value, therefore, the calibration coefficient is replaced with this lower limit guard value, thereby minimizing the effect that would be produced if the calculated calibration coefficient is not accurate.